Abstract
Despite the introduction of new therapies for multiple myeloma (MM), many patients are still dying from this disease and novel treatments are urgently needed. We have designed a novel hybrid molecule, called NEO214, that was generated by covalent conjugation of the natural monoterpene perillyl alcohol (POH), an inducer of endoplasmic reticulum (ER) stress, to rolipram (Rp), an inhibitor of phosphodiesterase-4 (PDE4). Its potential anticancer effects were investigated in a panel of MM cell lines. We found that NEO214 effectively killed MM cells in vitro with a potency that was over an order of magnitude stronger than that of its individual components, either alone or in combination. The cytotoxic mechanism of NEO214 involved severe ER stress and prolonged induction of CCAAT/enhancer-binding protein homologous protein (CHOP), a key pro-apoptotic component of the ER stress response. These effects were prevented by salubrinal, a pharmacologic inhibitor of ER stress, and by CHOP gene knockout. Conversely, combination of NEO214 with bortezomib, a drug in clinical use for patients with MM, resulted in synergistic enhancement of MM cell death. Combination with the adenylate cyclase stimulant forskolin did not enhance NEO214 impact, indicating that cyclic adenosine 3′,5′-monophosphate (AMP) pathways might play a lesser role. Our study introduces the novel agent NEO214 as a potent inducer of ER stress with significant anti-MM activity in vitro. It should be further investigated as a potential MM therapy aimed at exploiting this tumor’s distinct sensitivity to ER stress.
Highlights
Among the various tasks of the endoplasmic reticulum (ER) is proper protein folding and processing
To gain insight into the mechanisms of NEO214-induced cell death, we focused on the two processes that were known to be targeted by its individual components, i.e., inhibition of PDE4 enzymatic activity by Rp and aggravation of ER stress by perillyl alcohol (POH)
We have explored a novel ER stress-aggravators (ERSAs) combination for MM, based on the use of a newly created, chimeric molecule—NEO214—that turned out to harbor strong ERSA potency
Summary
Among the various tasks of the endoplasmic reticulum (ER) is proper protein folding and processing. The cell reacts to ER stress by initiating a defensive process, called the unfolded protein response (UPR), which pursues two objectives: first, in the case of moderate stress, the defensive module of this system attempts to neutralize or adapt to the insult and restore proper homeostasis. In the case of excessively aggravated stress, the UPR switches to its pro-apoptotic module and initiates apoptosis [1]. Among the executor proteins of the apoptotic component is CHOP (CCAAT/enhancer binding protein homologous transcription factor, called GADD153), a transcription factor that alters the transcriptional profile of cells and triggers a pro-apoptotic program [2]. Prolonged expression of CHOP is a key trigger for apoptosis, and this protein is commonly used as a marker to indicate that pro-apoptotic events of the UPR have been initiated [3]
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